UC San Diego
The recruitment of cellular regulators of transcription to sites of viral transcription at the beginning of human cytomegalovirus infection
- Author(s): Kapasi, Anokhi J.
- et al.
During human cytomegalovirus (HCMV) infection, transcription of viral genes is mediated by cellular RNA polymerase (RNAP) II. To understand how RNAP II is redirected towards viral transcription, I have characterized the regions of viral transcription, known as viral transcriptosomes, at immediate early (IE) times of the infection, analyzed alterations in several cellular components of transcription, as well as examined the role that the RNAP II kinases, cdk9 and cdk7, play in viral gene expression. By tracking cellular RNAP II and its kinase complexes, I have shown that there is a general upregulation of these cellular components of transcription in levels and activities. Several of these components colocalize with the input HCMV genome, viral major IE proteins, IE1-72 (IE1) and IE2-86 (IE2), within the first 8 hours of infection. These components include transcriptionally active RNAP II, cdk7, cdk9, and even regulators of chromatin remodeling. The sites of viral IE transcription are much more complex than was previously thought, and from this work a model for the establishment of the viral transcriptosomes has been developed. I also found that in addition to the presence of the input viral genome and input viral particle, initial formation of the viral transcriptosome requires both transcription and protein synthesis. In the specific case of cellular cdk9, efficient binding to cyclin T1 and continuous transcription are respectively required to recruit and maintain cdk9 at the viral transcriptosomes. Studies with inhibitors of cyclin-dependent kinase (cdk) activity have already been shown to be important for the establishment of the productive infection. In this dissertation, I have revealed a temporal role of cdk9 and cdk7 during the infection; a contribution at IE times of the infection for the establishment of the viral transcriptosomes and viral- specific hyperphosphorylation of RNAP II, and at early to late times of the infection for viral efficient viral protein production. These dual functions seem to correspond with two relocalization events for cdk9 and cdk7. The experiments described in this dissertation demonstrate various means by which the cellular components of transcription contribute to viral gene expression and to the progression of the productive HCMV infection